1. Technical Field
The present invention relates to a transport roller, a transport device and a printing apparatus.
2. Related Art
Heretofore, a variety of printers have been provided as printing apparatuses. In each of such printers, a recording medium (transported medium) such as a printing sheet is transported by a variety of rollers. To be more specific, the recording medium is transported to a printing unit by a transport roller and a driven roller, to perform printing for the recording medium in the printing unit, and to thereafter discharge the recording medium by a discharge roller and a driven roller.
In particular, the transport roller pinches the printing sheet between the driven roller and the transport roller, and is rotationally driven in this state, thereby moving the sheet in a sub-scanning direction perpendicular to a moving direction of a carriage. Hence, the transport roller is required to have high transport capability since the transport roller transports the printing sheet to a recording position with high accuracy, and further, sequentially sends a plurality of printing sheets in accordance with a printing speed.
In order to make the transport roller maintain large frictional force, Japanese Patent No. 3,271,048 discloses a technology for forming a large number of protrusions on a circumferential surface of a metal round bar by a perforation process.
However, in this technology, the protrusions are formed on the surface of such a shaft-like (columnar) bar along a circumferential direction thereof, and accordingly, a problem of poor workability is inherent therein. Moreover, since such a solid material is used, there is also a problem that, for example, total weight and cost of a printer using the transport roller are increased.
Based on such a background, in order to reduce cost in the solid shaft, JP-A-2006-289496 proposes that a metal plate is bent into a form of a cylinder-like (hollow) shaft (that is, a cylindrical shaft), and this cylindrical shaft is used in place of the metal solid round bar material.
In the case of bending a metal plate into a form of a cylindrical shaft, end surfaces of the metal plate are matched with each other, and accordingly, on the surface of the cylindrical shaft, a slight gap or a groove (seam) is formed across the overall length thereof.
Therefore, if the cylindrical shaft described in JP-A-2006-289496 is used, for example, as a transport roller of the printer, then a phenomenon occurs that lubricant (such as grease) supplied between the transport roller and a bearing that supports the transport roller flows through the seam by a capillary action.
Then, there occurs a problem that the lubricant permeates a region where the transport roller contacts with the recording medium (transported medium), and soils the recording medium with the lubricant.